Flow cytometric detection of MR1. 293T cells were transfected with boMR1 or mock-transfected and stained with a panel of anti human MR1 antibodies. Monoclonal antibody clone 20 stained transfected cells (B), but not mock-transfected cells (A). Isotype-matched clone 1 did not stain transfected cells (C). Ex vivo cell suspensions from spleen (D–F), thymus, ileum, colon and prescapular lymph node (not shown) were stained with anti MR1 clone 20 or with anti bovine CD3. Ex vivo bovine PBMC were double stained with anti MR1 clone 20 and anti bovine CD3, CD14 or CD21 (G–I). All stainings were performed using a protocol that stains intracellular plus cell surface molecules.